ESP-01 not responding on MB1280 fanout - STM32H747I-DISCO
Hi ST Community — quick question about the MB1280 fanout and the ESP-01 socket.
I’m trying to get UART comms between an STM32H747I-DISCO and an ESP-01 (plugged into the MB1280 ESP-01 socket) but I can’t get any response from the ESP.
Setup
STM32H747I-DISCO (MB1248) + MB1280 fanout (3V3-C01 rev)
ESP-01 in the dedicated ESP-01 socket on MB1280
STM32 ↔ ESP via STMod+ P2 (20-pin) — USART2 on PD5 (TX) / PD6 (RX)
USART2: 115200 baud, RX handled with interrupts
What happens
STM32 transmits AT commands (verified on a logic analyzer).
ESP-01 powers.
But: STM32 receives zero bytes — no boot messages, no AT replies. Tried other baud rates (9600, 74880, 57600) — nothing.
What I measured
GPIO0 (ESP-01 pin 5) reads 0 V (GND) with a multimeter.
That explains it: GPIO0 = LOW at boot → ESP goes into flash/bootloader mode, so it won’t run AT firmware. The LED behavior also matches (LED stays on in flash mode).
Questions
How is GPIO0 wired on the MB1280 at the ESP-01 socket? Is it tied to GND by default?
Is there a jumper, DIP switch, or solder bridge on the MB1280 to change GPIO0 to HIGH at boot? If so, where is it located? (I couldn’t find it in UM2411.)
If there’s no configurable option, is the recommended workaround simply to add a 10 kΩ pull-up from GPIO0 to 3.3 V?
What I’ve confirmed
ESP gets stable 3.3 V (~200 mA available)
CH_PD tied to 3.3 V (so module boots)
STM32 TX actually sends the AT commands (logic analyzer)
ESP-01 hardware appears functional (boot LED sequence present)
What fails
GPIO0 stuck at 0 V (keeps module in bootloader)
No UART bytes received / no AT replies
If anyone here has MB1280 + ESP-01 experience, could you confirm how GPIO0 is configured and where to change it (jumper / solder pad)?
Thanks a lot!